Conventionally, in the manufacture of semiconductor devices, micro-processing by lithography using a photoresist composition has been carried out. The micro-processing is a processing method including forming a thin film of a photoresist composition on a silicon wafer, irradiating actinic rays such as ultraviolet rays through a mask pattern depicting a pattern for a semiconductor device, developing it to obtain a resist pattern, and etching the silicon wafer using the resist pattern as a protective film. However, in recent progress in high integration of semiconductor devices, there has been a tendency that shorter wavelength actinic rays are being used, i.e., ArF excimer laser beam (193 nm) has been taking the place of KrF excimer laser beam (248 nm). Along with this change, influences of random reflection and standing wave off a substrate have become serious problems. Accordingly, it has been widely studied to provide an anti-reflective coating between the photoresist and the substrate (Bottom Anti-Reflective Coating, BARC).
As the anti-reflective coating, inorganic anti-reflective coatings made of titanium, titanium dioxide, titanium nitride, chromium oxide, carbon or α-silicon and organic anti-reflective coatings made of a light-absorbing substance and a high molecular compound are known. The former requires an installation such as a vacuum deposition apparatus, a CVD (chemical vapor deposition) apparatus or a sputtering apparatus. In contrast, the latter is considered advantageous in that it requires no special installation so that many studies have been made. For example, mention may be made of the acrylic resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule as disclosed in U.S. Pat. No. 5,919,599 and the novolak resin type anti-reflective coating having a hydroxyl group being a crosslinking reaction group and a light absorbing group in the same molecule as disclosed in U.S. Pat. No. 5,693,691, and so on.
The physical properties desired for organic anti-reflective coating materials include high absorbance to light and radioactive rays, no intermixing with the resist layer (being insoluble in resist solvents), no diffusion of low molecular substances from the anti-reflective coating material into the topcoat resist upon coating or heat-drying, and a higher dry etching rate than the resist. They are described in, for example, Proc. SPIE, Vol. 3678, 174-185 (1999) and Proc. SPIE, Vol. 2195, 225-229 (1994). Further, it has been required that anti-reflective coating materials have a property that the margin of depth of focus can be over a wide range or a property that the resolution can be improved.
The margin of depth of focus means a width of total depth range in which a resist pattern can be kept in a practicable state when a focus is displaced upward or downward from the optimum focus position. The broader the width is, the higher the level of additional coverage in the production process is. For example, one of techniques for improving the margin of depth of focus is disclosed in Japanese Patent Laid-open No. Hei 6-348036.
The production of semiconductors includes a process for forming a resist pattern by selectively exposing a photoresist layer formed on an object to be processed, such as a silicon wafer with light and then developing. During the exposure, the focus of irradiated light for exposure is sometimes displaced for the optimum position. This is caused by curvature of image plane, deterioration in the reproducibility of focus position (detection, stage) or lowering in stability of focus control (heat, environment) from the aspect of manufacturing equipments, and difference in level on devices formed on a wafer, global inclination of a wafer or local unevenness on a wafer from the aspect of wafers, and the like. The above-mentioned displacement from the optimum focus position causes deformation of resist patterns, such as thinned pattern, thereby causing improper forming of resist patterns, such as pattern collapse. Consequently, there causes a problem that resist patterns can not be formed in a high dimensional accuracy. In particular, in a micro-processing with irradiated light having a wavelength of 193 nm, thinned pattern or pattern collapse resulting from displacement from the optimum focus position becomes problems. Under the present status of the art, there is a growing demand for anti-reflective coating materials having a property that can suppress to a low level influence on resist pattern formation due to displacement from the focus of irradiated light for exposure, that is, a property that enables margin of depth of focus to be widen.
Further, with high integration of semiconductor devices, there is a growing demand for anti-reflective coating materials having a higher resolution, that is, a property that makes it possible to form rectangular resist patterns with finer pattern size.
In the meantime, Japanese Patent Laid-open No. Hei 11-72925 proposes a method for forming a resist pattern having a perpendicular side wall and a good rectangular section in order to inhibit any film loss of the resist pattern and to form the resist pattern in a high resolution and high dimensional accuracy. The method comprises forming a pattern by using an undercoat layer composition containing a compound having a substituent which is decomposed by an acid to then afford an alkali-soluble group, and an acid generator which produces the acid, and dissolving and removing exposed portions on the undercoat layer formed from the composition by a developer; or the method comprises forming a pattern by using an undercoat layer composition containing a compound having a substituent which is crosslinked by an acid, and an acid generator which produces the acid, and dissolving and removing unexposed portions on the undercoat layer formed from the composition by a developer.
However, the undercoat layer composition disclosed in the above-mentioned publication is developed for anti-reflective coatings on the assumption that a part of the undercoat layer which a resist thereon is removed by exposure and development is removed by wet etching. Therefore, this can not be necessarily applied as such for a composition for forming anti-reflective coating for pattern forming on the assumption that a part of the undercoat layer which a resist thereon is removed by exposure and development is removed by dry etching, or for such a composition containing a crosslinking agent. It is generally known that performance and properties on micro-processing by lithography in a composition for forming anti-reflective coating containing a crosslinking agent are different from those in a composition for forming anti-reflective coating containing no crosslinking agent. Further, the above-mentioned publication does not propose or suggest concrete improvement measures on margin of depth of focus and high resolution that become problem in resist pattern formation.
Under the above-mentioned circumstances, an object of the present invention is to provide a composition for forming anti-reflective coating that can attain broad margin of depth of focus and high resolution on the assumption that pattern formation is carried out by dry etching.
The present invention provides a composition for forming anti-reflective coating which inhibits efficiently reflection for using it as anti-reflective coating particularly when irradiated light having a wavelength of 193 nm is used in micro-processing, further which improves an adhesion with a photoresist, has broad margin of depth of focus and can attain high resolution. That is, an object of the present invention is to provide a composition for forming anti-reflective coating for use in lithography which has a high prevention effect of reflected light, causes no intermixing with a resist layer, provide an excellent resist pattern and broad margin of depth of focus, and has a higher dry etching rate than resists; and a method for forming resist pattern by using the composition for forming anti-reflective coating.